Epoxy resin composition

ABSTRACT

A solvent-free epoxy resin matrix composition comprising: (a) a liquid epoxy resin or a liquid mixture of epoxy resins, (b) a benzylidenamine compound, (c) an aliphatic or cycloaliphatic primary monoamine and/or disecondary diamine; and (d) a catalytically curing tertiary amine. The epoxy resin matrix composition is used as an impregnating resin to form impregnated fiber composite materials.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of International ApplicationPCT/EP2004/050440 filed Apr. 5, 2004 which designated the U.S. and whichclaims priority to Swiss Pat. App. No. 0625/03 filed Apr. 7, 2003. Thenoted applications are incorporated herein by reference.

The present invention relates to a fibre composite impregnated with anepoxy resin matrix and comprising a benzylidenamine compound, to a fibrecomposite laminate produced from the said fibre composite, to the use ofa benzylidenamine compound for improving fibre composite properties, andto an epoxy resin matrix comprising a benzylidenamine compound.

For producing storage-stable prepregs it is known to use pre-reactedepoxy resin mixtures which are still curable, i.e. B-stage resins, orpre-extended epoxy resins, in other words epoxy resins of relativelyhigh molecular mass. Resin systems of this kind are either solid or ofhigh viscosity, so that impregnation of fibre materials using theseresins necessitates organic solvents, or they have to be applied atelevated temperature from the melt to the fibre material, or else inliquid form, with particular advantage.

From EP 133 154, for example, it is known, to produce prepregs, asresin, to use liquid epoxy resins with a curative mixture comprisingcertain monoamines and/or diamines and a catalytic tertiary amine.

The flexibility of the prepregs known to date, however, is frequentlytoo low, leading for example to formation of dust during stamping.Attempts to flexibilize the prepregs by means of a flexibilizer such asbenzyl alcohol, however, lead to an inadequately short prepreg stabilityof 1-2 days and also often to tacky surfaces. Moreover, steadilyincreasing requirements are being noted as regards the stability(storage at room temperature for longer than 6 days) and the processingconditions (dry surface, extended latency times).

It has now been found that, surprisingly, the properties of fibrematerials impregnated with a curable, liquid, solvent-free epoxy resinor epoxy resin mixture which comprises as curative a specific aminemixture based on monoamines can be improved by the addition of abenzylidenamine compound, preferably benzylidenebenzylamine.

The present invention accordingly provides a fibre composite impregnatedwith a curable, solvent-free epoxy resin matrix, comprising

-   (a) a liquid epoxy resin or a liquid mixture of epoxy resins,-   (b) a compound obtainable by reacting a benzaldehyde of the formula    I

in which R¹ is hydrogen, hydroxyl, C₁-C₅alkyl or C₁-C₅alkoxy with aprimary amine, and as curing agent a mixture composed of

-   (c) an aliphatic or cycloaliphatic primary monoamine and/or    disecondary diamine and-   (d) a catalytically curing tertiary amine, the curable epoxy resin    matrix containing from 0.15 to 0.8 amine hydrogen equivalent of the    amine component (c) and from 0.01 to 0.1 mol of the tertiary    amine (d) per epoxide equivalent of the epoxy resin (a).

Primary amines for preparing the benzylidenamine compound of component(b) are, for example, aliphatic, cycloaliphatic or araliphatic amines.

Aliphatic amines derive for example from C₁-C₄₀alkyl radicals, such asmethyl, ethyl, isopropyl, n-propyl, n-butyl, isobutyl, sec-butyl,tert-butyl, and also the various isomeric pentyl, hexyl, heptyl, octyl,nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,hexadecyl, heptadecyl and octadecyl groups.

Cycloaliphatic amines derive for example from C₃-C₁₂cycloalkyl radicals,such as preferably C₅-C₈cycloalkyl or with particular preference C₅- orC₆cycloalkyl. Some examples are cyclopentyl, methylcyclopentyl,cyclohexyl, cycloheptyl and cyclooctyl.

Araliphatic amines derive for example from compounds containing 7 to 12carbon atoms and with particular preference from compounds containing 7to 10 carbon atoms. The compounds in question can be, for example,benzyl, phenethyl, 3-phenylpropyl, α-methylbenzyl, 4-phenylbutyl andα,α-dimethylbenzyl.

The aforementioned radicals can where appropriate be substituted and canalso-contain a hydrocarbon chain which is interrupted by oxygen.Examples of oxygen-interrupted hydrocarbon chains are polyoxyalkyleneradicals, such as polyoxyethylene or polyoxypropylene.

Specifically suitable polyamines are, for example,bis(4-aminophenyl)methane, aniline-formaldehyde resins,propane-1,3-diamine, 2,2-dimethyl-1,3-propanediamine(neopentanediamine), hexamethylenediamine, diethylenetriamine,bis(3-aminopropyl)amine, N,N-bis(3-aminopropyl)methylamine,triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine,2,2,4-trimethylhexane-1,6-diamine, m-xylylenediamine, 1,2- and1,4-diaminocyclohexane, bis(4-aminocyclohexyl)methane,bis(4-amino-3-methyl-cyclohexyl)methane,2,2-bis(4-aminocyclohexyl)propane and3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophoronediamine),polyaminoimidazolines and polyaminoamides, such as those formed fromaliphatic polyamines and dimerized or trimerized fatty acids, forexample. Further suitable amines include the polyoxyalkyleneamines fromTexaco which are known as Jeffamines® such as Jeffamine® EDR148, D230,D400 or T403, for example.

Of specific preference are benzylamine and Jeffamine® D230.

The reaction of the compound (I) with primary amine takes place in a waywhich is known to the person skilled in the art, by the addition, forexample, to the amine compound in a solvent of the compound (I) and theseparation of the product obtained. The reaction takes place preferablyin an equimolar ratio of the primary amino groups to the compound (I).

Preferred as component (b) are compounds of the formula II

in which R¹ is hydrogen, hydroxyl, C₁-C₅alkyl or C₁-C₅alkoxy;

-   n is a number which is 1 or more; and-   A is an n-valent radical derived from an aliphatic, cycloaliphatic    or araliphatic compound having at least n primary amino groups.

Preferably A is an n-valent C₁-C₄₀alkyl radical, which optionally can beinterrupted by oxygen, or is a C₃-C₈cycloalkyl or C₇-C₁₀aralkyl radical.

Preferably n is one of the numbers 1 to 10 and with particularpreference it is 1 or 2.

In the curable epoxy resin matrix suitable for impregnation there ispreferably from 0.3 to 20% by weight, more preferably from 0.3 to 8% byweight, based on components (a), (c) and (d), of component (b),preferably benzylidenebenzylamine. Also advantageous are amounts ofcomponent (b) of greater than 1.5% and in particular greater than 4% byweight.

In the curable epoxy resin matrix suitable for impregnation there ispreferably from 0.2 to 0.7 amine hydrogen equivalent of the. aminecomponent (c) and from 0.02 to 0.06 mol of the tertiary amine (d) perepoxide equivalent.

In one preferred embodiment the fibre composite is impregnated with anepoxy resin matrix, with component (c) being a primary monoamine.

Examples of suitable components (a) include the liquid epoxy resinsbased on bisphenol A or F or based on phenol novolaks or mixturesthereof in any proportion. They can be mixed with a reactive diluent,such as phenyl or cresyl glycidyl ether, butanediol diglycidyl ether ordiglycidyl hexahydrophthalate, for example, preferably in an amount of3-50% by weight, based on the total amount of the epoxy resins, or withdiglycidylaniline, preferably in an amount 3-20% by weight, based on thetotal amount of the epoxy resins. Further suitable mixtures of epoxyresins include triglycidyl-p-aminophenoi andtetraglycidyl-p,p′-diaminodiphenylmethane, which may be in the form of amixture with butanediol diglycide or diglycidylaniline.

The stated epoxide compounds can also be used in any desired mixtureswith one another or with solid epoxy resins which are soluble in theepoxy resin mixture, provided that the viscosity of the end mixture atroom temperature is less than 12 000 mPa.s, preferably less than 6000mPa.s, more preferably less than 1500 mPa.s, the viscosity determinationbeing carried out in accordance with Brookfield using spindle 3 at 50rpm and at 25° C.

Examples of compounds suitable as primary monoamine (c) includebenzylamine, cyclo-hexylamine, ethanolamine, 2-ethylhexylamine,2-phenylethylamine, 3-(2-ethylhexoxy)propylamine, n-octylamine,2-butoxyethylamine, 2-(2-hydroxyethoxy)ethyl-1-amine,3-isopropoxypropyl-1-amine or 3-amino-2,2-dimethylpropan-1-ol.

Examples of suitable disecondary diamines (c) include piperazine,N,N′-dicyclohexylhexamethylene-1,6-diamine andN,N′-bis(β-cyanoethyl)hexamethylene-1,6-diamine.

The aforementioned primary monoamines and disecondary diamines are knowncompounds and are largely available commercially.

The tertiary amines (d) which are used as catalytic curing agents arelikewise known curing agents for epoxy resins, and some of them areavailable commercially. In addition to the compounds specified there itis also possible to use the compounds disclosed in EP 018 949 or theknown imidazole compounds of the formulae

in which R₁ and R₂ independently of one another are each a hydrogenatom, methyl, ethyl or phenyl. The imidazole compounds of the specifiedformulae are preferred catalytic curing agents.

As reinforcing fibres for the fibre composite of the invention it ispossible to use the customary fibres which are used for fibrereinforcement of materials. These can be organic or inorganic fibres,natural fibres or synthetic fibres, and may be present in the form ofwovens or non-crimp fabrics, nonwoven webs or mats, and also in the formof fibre strands (rovings), or as staple fibre or continuous fibre. Asreinforcing fibres use is made, for example, of glass, boron, carbon ormetal fibres and also aramide fibres, high-strength polyester fibres ornatural fibres from cotton or spun rayon. Such fibres and wovens madefrom them are available commercially.

These fibres or wovens can be coated with the solvent-free epoxy resinmixture by the standard impregnating methods, by brushing, spraying, ordipping, by means of extrusion or, in the case of continuous fibres, bythe precision filament winding method.

The fibre materials coated with the matrix resin can be dried in air atroom temperature, in which case the matrix resin is gradually convertedto the still-meltable or -curable B stage and what are known as prepregsare obtained. Since the matrix resin used for impregnating issolvent-free, there is no need, moreover, for the process step ofremoving the solvent without residue from the fibre composite prior tofinal curing, which is necessary in order that no pores or holes areformed in the cured composite as a result of the evaporation of residualsolvent.

The production of prepregs from the fibre composite of the invention istherefore also associated with the advantage that neither for theevaporation of the solvent nor for the pre-extension of the resin isthere any need for the corresponding process steps, and that there is noheat energy expense required.

The fibre composite of the invention is preferably in the form ofprepregs, which can be used to produce laminates in conventionalfashion.

The prepregs of the invention can be cured to completely at temperaturesbelow 120° C. and are therefore advantageously suitable for producingfibre composite systems with other materials, particularly those whichdo not withstand temperatures above 120° C. well, such as wood orplastics with a low softening point, such as ABS polymers, polyethyleneor PVC, for example.

The present invention accordingly further provides a fibre compositesystem, in particular a fibre composite laminate, which is obtained fromthe fibre composition of the invention together where appropriate withother materials, with shaping and crosslinking of the resin matrix.

The present invention additionally provides for the use ofbenzylidenebenzylamine for improving the properties of a fibre compositecomprising an epoxy resin and as curing agent a mixture composed of analiphatic or cycloaliphatic primary monoamine and/or disecondary diamineand a catalytically curing tertiary amine.

Preference is given to the use of benzylidenebenzylamine for improvingthe flexibility of prepregs and/or the processing time of the laminate(increasing the latency time). The preferred use ofbenzylidenebenzylamine corresponds to the preferences described earlieron above for the fibre composite comprising epoxy resin. Particularadvantage for improving the flexibility of prepregs is given to the useof 4-8% by weight of benzylidenebenzylamine.

The present invention further provides an epoxy resin matrix comprisinga liquid epoxy resin or a liquid mixture of epoxy resins,benzylidenebenzylamine and as curing agent a mixture composed of analiphatic or cycloaliphatic primary monoamine and/or disecondary diamineand a catalytically curing tertiary amine.

A preferred epoxy resin matrix corresponds to the preferences describedearlier on above for the fibre composite comprising epoxy resin.

Preparation Examples for Benzylidene Compounds

A 750 ml sulphonating flask provided with stirrer, internal thermometer,dropping funnel and reflux condenser is charged with 50 g (0.217 mol) ofJeffamine® D 230, and 200 ml of ethanol are added with stirring. Afterthis solution has been stirred for 30 minutes 40.3 g (0.379 mol) ofbenzaldehyde are added over the course of 15-20 minutes at an internaltemperature of 23-24° C. This reaction mixture is heated to boilingunder reflux at an internal temperature of 75-78° C. over the course of15 minutes. After 2.5 hours under reflux (internal temperature: 78° C.)the yellow solution is cooled to room temperature. 50 to 100 g ofanhydrous sodium sulphate are added to this solution at room temperatureand the mixture is stirred at room temperature for one hour more.Following the removal of the sodium sulphate by filtration the majorfraction of the solvent is removed by means of a rotary evaporator.Residual ethanol is removed under reduced pressure at 45° C. and apressure of 3 mBar in the course of three hours. 83.3 g of a brownishoil are isolated.

¹H-NMR: (CDCl₃)

δ=0.92 ppm (m); 1.1 ppm (m); 3-3.8 ppm (m); 7.42 ppm (s); 7.72 ppm (m)Integral ratio: 7.16:9.8:3.2:2:1

IR (Pure):

3060.19 cm⁻¹, 2966.99 cm⁻¹ (intense); 2924.27 cm⁻¹(intense), 2862.14cm⁻¹(intense); 1700.97 cm⁻¹(traces),1646.60 cm⁻¹ (intense), 1576.70cm⁻¹, 1444.66 cm⁻¹, 1374.76 cm⁻¹, 1106.80 cm⁻¹ (intense, broad), 753.40cm⁻¹, 691.26 cm⁻¹

A 750 ml sulphonating flask provided with stirrer, internal thermometer,dropping funnel and reflux condenser is charged with 50 g (0.217 mol) ofJeffamine® D 230, and 200 ml of ethanol are added with stirring. Afterthis solution has been stirred for 30 minutes 46.4 g (0.38 mol) ofsalicylbenzaldehyde are added over the course of 15-20 minutes at aninternal temperature of 22° C., whereupon an internal temperature of 34°C. is established. After a further 30 minutes of stirring thetemperature dropped to 26° C. The dark-yellow reaction solution thusobtained is heated to 77° C. to 78° C. over the course of 20 minutes, sothat reflux comes about. The progress of the reaction is monitored bymeans of thin-layer chromatography (mobile phase: toluene, silica gel onglass, Merck, developer: potassium permanganate solution). After fourhours there is no further change in the pattern, and this is taken to becomplete conversion. After it has cooled to room temperature, thisreaction solution is admixed with about 50-100 g of anhydrous sodiumsulphate and stirred for one hour thereafter. After the drying agent hasbeen filtered off the major fraction of the solvent is removed by meansof a rotary evaporator. Some residues are removed under a high vacuum(45° C./3 mBar, 3 hours). 89.7 g of a yellow oil are isolated.

TLC: Salicylbenzaldehyde r_(f): 0.42; Jeffamine D 230: r_(f1): 0.07;r_(f2): 0.14; r_(f3): 0.22 Isolated product: r_(f1): 0.1, r_(f2): 0.28

¹H-NMR: (CDCl₃)

δ=0.96 ppm (m,4); 1.22 ppm (m, 3.7); 3.48 ppm (m, 7.3); 6.76 ppm (m,3.2); 6.9 ppm (m, 1), 7.23 ppm (CDCl₃); 8.3 ppm (m,1.25); 8.3 ppm (s,traces)

Integral ratios of the signals between d=0 and 15 ppm):

-   -   4:4:7.3:3.2:1:1.1:1.25

IR (Pure)

3500-3100 cm⁻¹(broad), 3056.3 cm⁻¹(weak), 2966.99 cm⁻¹ (intense),2928.16 cm⁻¹ (intense); 2858.25 cm⁻¹ (intense), 2788 cm⁻¹ (weak),2733.98 cm⁻¹ (weak), 2664.08 cm⁻¹ (weak), 1634 cm⁻¹ (intense), 1580.58cm⁻¹ (moderate), 1495.15 cm⁻¹, 1456.31 cm⁻¹, 1413.59 cm⁻¹, 1378.64 cm⁻¹,1330 cm⁻¹, 1277.67 cm⁻¹, 1207.77 cm⁻¹, 1145.63 cm⁻¹, 1114.56 cm⁻¹,1025.24 cm⁻¹, 978.64 cm⁻¹, 932.04 cm⁻¹, 904.85 cm⁻¹, 846.60 cm⁻¹, 753.40cm⁻¹, 737.86 cm⁻¹

EXAMPLE 1

100 g of an epoxy resin based on bisphenol A, having an epoxide contentof 5.3 equivalents/kg, and 5.9 g of benzylidenebenzylamine are admixedwith an amine mixture made up of 15 g of benzylamine (0.53 N—Hequivalent/epoxide equivalent) and 3 g of2,4,6-tris(dimethylaminomethyl)phenol (0.021 mol/epoxide equivalent) andthe components are mixed with one another until the mixture is free ofstreaks. This resin mixture is used to impregnate sections of glasswoven (Interglasgewebe 92146 from Interglas-Textil GmbH/DE) (resincontent 30-35% by weight). After one day the sections of glass wovenhave a dry surface, are very flexible, and exhibit a resin flow of about13% after 6 days of storage at 20-25° C. The prepregs can be stampedwithout forming dust and the Tg after 20 minutes' curing at 110° C. is63° C.

The resin flow determination is carried out as follows:

2 square pieces of prepreg with an edge length of 5 cm, for example, areweighed (=G1), laid precisely on top of one another, then insertedbetween 2 release papers or sheets into a press preheated to 100° C.This press is immediately closed to a pressure of 2 MPa. After 5 minutesthe resulting laminate is removed from the hot press and the resin whichis flowed out along the edge of the laminate is cut off. The laminate isweighed again (=G2). The difference in weight between G1 and G2,expressed in %, gives the “flow”.

COMPARATIVE EXAMPLE

Prepregs are produced in analogy to Example 1 but without the additionof benzylidenebenzylamine. After one day of storage at 20-25° C. suchprepregs are very brittle and form large amounts of dust duringstamping.

EXAMPLE 2

The viscosity of epoxy resin mixtures as per the table below ismeasured.

0% 0.3% 1.5% 4.8% A) Epoxy resin (5.3 eq/kg) 100 100 100 100 Benzylamine15 15 15 15 2,4,6- 3 3 3 3 Tris(dimethylaminomethyl)- phenolBenzylidenebenzylamine 0.354 1.77 5.9 Viscosity at 60° C. 7160 3470 28201310 after 30 minutes B) Epoxy resin (5.3 eq/kg) 100 100 100 Benzylamine15 15 15 2,4,6- 3 3 3 Tris(dimethylaminomethyl)- phenol Compound A10.354 1.77 5.9 Viscosity at 60° C. 2430 2250 1050 after 30 minutes C)Epoxy resin (5.3 eq/kg) 100 100 100 Benzylamine 15 15 15 2,4,6- 3 3 3Tris(dimethylaminomethyl)- phenol Compound A2 0.354 1.77 5.9 Viscosityat 60° C. 2900 2430 1400 after 30 minutes

The addition of benzylidenebenzylamine or a benzylidenamine compoundaccording to Example A1 and A2 leads to a marked retardation of theincrease in viscosity as compared with the samples which do not containthe stated compounds.

1. A fibre composite impregnated with a curable, solvent-free epoxyresin matrix composition, said composition comprising: (a) a liquidepoxy resin or a liquid mixture of epoxy resins, (b) a benzylidenaminecompound obtained by reacting a benzaldehyde of the formula (I)

 in which R¹ is hydrogen, C₁-C₅ alkyl or C₁-C₅ alkoxy, with a primaryamine, (c) an aliphatic or cycloaliphatic primary monoamine and/ordisecondary diamine, and (d) a catalytically curing tertiary amine, thecurable epoxy resin matrix composition containing from 0.15 to 0.8 aminehydrogen equivalent of the amine component (c) and from 0.01 to 0.1 molof the tertiary amine (d) per epoxide equivalent of the epoxy resin (a).2. The fibre composite according to claim 1, containing from 0.3 to 20%by weight, based on components (a), (c) and (d), of the benzylidenaminecompound.
 3. The fibre composite according to claim 1, containing from0.2 to 0.7 amine hydrogen equivalent of the amine component (c) and from0.02 to 0.06 mol of the tertiary amine (d) per epoxide equivalent. 4.The fibre composite according to claim 1, wherein component (c) is analiphatic or cycloaliphatic primary monoamine.
 5. The fibre compositeaccording to claim 1, wherein the benzylidenamine compound isbenzylidenebenzylamine.
 6. A fibre composite system, produced from thefibre composite according to claim 1 together with wood or plasticshaving a low softening point.
 7. A solvent-free epoxy resin matrixcomposition comprising: (a) a liquid epoxy resin or a liquid mixture ofepoxy resins, (b) a benzylidenamine compound obtained by reacting abenzaldehyde of the formula (I)

 in which R¹ is hydrogen, C₁-C₅ alkyl or C₁-C₅ alkoxy with a primaryamine, (c) an aliphatic or cycloaliphatic primary monoamine and/ordisecondary diamine, and (d) a catalytically curing tertiary amine. thecurable epoxy resin matrix composition containing from 0.15 to 0.8 aminehydrogen equivalent of the amine component (c) and from 0.01 to 0.1 molof the tertiary amine (d) per epoxide equivalent of the epoxy resin (a).8. The epoxy resin matrix according to claim 7, containing, based on thetotal amount of epoxy resin and curing agent, from 0.3 to 20% by weightof the benzylidenamine compound obtained by reacting a benzaldehyde ofthe formula (I)

in which R¹ is hydrogen, C₁-C₅ alkyl or C₁-C₅ alkoxy with a primaryamine.